1. Field of the Invention
The present invention relates to an ultrasonic transceiver which is installed to, for example, a vehicle such as an automobile or the like and adapted to detect that the vehicle is near to obstacles when the vehicle is parked or turned, and an ultrasonic clearance sonar using the ultrasonic transceiver.
2. Description of the Related Art
An ultrasonic clearance sonar can announce an alert to draw driver's attention to obstacles around the vehicle in accordance with each distance between the vehicle and each obstacle.
The ultrasonic clearance sonar has an ultrasonic transceiver also called to as “microphone” and is configured to cause the transceiver to transmit ultrasonic waves to a space around the vehicle, and measure each distance from the vehicle (ultrasonic transceiver) to each obstacle on the basis of each time for which each echo, that is, each ultrasonic wave reflected from each obstacle is returned to the ultrasonic transceiver. The ultrasonic clearance sonar announces an alert when at least one of the measured distances is reached to a predetermined value.
One conventional method of detecting a trouble occurring in the ultrasonic transceiver, such as disconnection therein or the like, uses the decay time of the reverberation waveform, that is, the waveform obtained after the transmission of the ultrasonic wave, one conventional method which is disclosed in the Japanese Patent Publication No. 2002-209294.
The conventional method of detecting the trouble of the ultrasonic transceiver by using the reverberation waveform cannot accurately judge that the ultrasonic transceiver is abnormal because of the oscillation of the waveform.
Namely, the reverberation is caused by an inertia oscillation of the ultrasonic transceiver, and the inertia oscillation is composed of an oscillation of an ultrasonic transmitting surface of the ultrasonic transceiver and that of a cylindrical tubular side wall, which are synthesized with each other.
The oscillation of the tubular side wall of the synthesized oscillations causes the inaccurate judgment of the ultrasonic clearance sonar. This reason is described hereinafter.
That is, the conventional ultrasonic transceiver comprises a housing having a plate-like bottom portion and a tubular side wall extending therefrom so that the bottom portion and the tubular side wall provide a cavity therebetween. The conventional ultrasonic transceiver also has a piezoelectric element mounted on an inner side of the bottom portion, and a rubber member as an oscillation absorption member with which an outer peripheral portion of the tubular side wall is covered.
Therefore, with the ultrasonic transceiver disposed to a bumper of a vehicle, foreign particles such as wax particles and so on are easily adhered on the outer peripheral portion of the tubular side wall. The adhered particles have an affect on the oscillation of the oscillation absorption member of the tubular side wall, and cause the reverberation waveform to be unstable, making it impossible to accurately judge that the ultrasonic transceiver is abnormal.
Therefore, there is a need for preventing foreign particles, such as wax particles from being adhered on an oscillation absorption member so as to inhibit a change of the oscillation of a tubular side wall of the ultrasonic transceiver, and to allow an ultrasonic clearance sonar to accurately judge that the ultrasonic transceiver is abnormal on the basis of the reverberation waveform.